Todd Fisher is letting his niece, Billie Lourd, "breathe."
ET's Nancy O'Dell sat down with Todd in Los Angeles on Wednesday, where he opened up about the tragic December deaths of his sister, Carrie Fisher, and their mother, Debbie Reynolds -- and revealed how Carrie's daughter has been dealing with the "horrible loss."
EXCLUSIVE: Todd Fisher Says Mom Debbie Reynolds 'Asked for Permission' to Go After Sister Carrie's Death
"Billie is 24 years old. She's dealing with two gigantic losses," Todd shared. "These two girls -- my girls, my mother and my sister, were big, big personalities [with a] big influence on Billie, myself, many people."
"There's a vacuum in the room and she's feeling it and we're all feeling it. It's just that I'm 59 and I have no choice but to step up and put this stuff forward," he continued. "I'm letting [Billie] breathe, you know? She needs to breathe. She needs to step back from all of this loss."
Fisher died on Dec. 27 at age 60, after going into cardiac arrest on a flight from London to Los Angeles a week earlier. Her mother, Reynolds, 84, died one day later, on Dec. 28.
"When I was standing in the room the day after my sister died and we're in the hospital and my mother was dying, I mean, I was more heartbroken watching my niece than I was for myself," Todd recalled. "It was heart wrenching. The idea that somebody would have to deal with that kind of a loss back to back, moment to moment -- I mean we'd just had this horrible loss and then here you are just a handful of hours later standing in a different hospital in a different room. It was astounding."
WATCH: Billie Lourd Pays Tribute to Mother Carrie Fisher With Heart-Wrenching Flashback Photo
"But she's also genetically Carrie and Debbie," Todd noted, before praising Billie's father, talent agent Bryan Lourd. "I don't want to leave Bryan Lourd out of this. He's an awesome father and if it wasn't for him right now, we would be in a much tougher position. He has supported her beautifully."
"You take those genes, and I think you've created a pretty powerful gal... and she is a lot more like my mother even than Carrie," he added. "You know, she's a little like Carrie but she's a lot like my mother, which means she's going to be another Molly Brown."
A public memorial for Debbie and Carrie -- who were laid to rest in January -- is set for March 25 at the Freedom Theater at Forest Lawn Cemetery Hollywood Hills in Los Angeles (and will be livestreamed on DebbieReynolds.com). While Todd says Billie wanted to pay tribute to her mother and grandmother, it was just too difficult.
"She said at one point she was gonna sing 'Tammy,' my mother's hit, and I was like, 'I don't know how you could do that. I couldn't do it,' and we started having reality checks on these things. She realized, 'I'd be lucky to sit through this," he revealed. "I can assure you that there isn't going to be a dry eye in the house at different times."
EXCLUSIVE: Billie Lourd Is Handling Her Family’s Loss ‘Very Well,’ Says ‘Scream Queens’ Co-Star Glen Powell
"Hopefully it's a roller coaster, where we have laughs and all of these things. It is a true memorial in the sense that you'e looking at all these real moments, and then you feel that loss, so you're going to cry. But there's also this beauty to it," he shared. "My mother is probably the heaviest contributor to this. She did the photography."
In addition to her family, Billie has also been leaning on her rumored boyfriend, Taylor Lautner, for support. Shortly after Carrie and Debbie's heartbreaking deaths, the 25-year-old actor whisked Billie away to Mexico for a little R&R.
See more in the video below.