The members of Migos - Offset, Quavo and Takeoff - at the 2018 Met Gala. Picture: Reuters

Offset had a R1.8 million chain stolen from his hotel room after the Met Gala.

The Migos rapper and his pregnant fiancee Cardi B stayed at the Hotel Sixty after the fashion extravaganza on Monday and when they checked out, they forgot to take the diamond necklace with them.

WATCH: Cardi B accidentally reveals baby's gender

According to the New York Post newspaper's Page Six column, the 'Culture II' rapper realised his chain was missing several hours later when he landed in Atlanta on Tuesday, so contacted his manager, Danny Zook, who was still at the hotel, but when staff searched the vacated suite, it was nowhere to be seen.

A source told the news outlet: "They had left the door open so people could come in and out of the room.

"The door was left open even when they weren't in the room."

According to TMZ, the chain was last seen on a coffee table in the room.

Police have confirmed they are currently investigating the theft and are currently checking security cameras near the elevator of the hotel.

Meanwhile, Cardi recently confirmed she and Offset are expecting a baby girl.

Speaking on 'The Howard Stern Show' on Wednesday, she simply said: "I'm having a girl."

The 25-year-old rapper had previously hinted at her unborn baby's sex when she spoke to reporters at the Met Gala, when she spoke about how feisty the tot is already.

She said: "Oh, she wants to fight me! [My dress weighs] about 35 pounds plus baby. It's OK though, I used to go up the project stairs. Shorty weighs three and a half pounds. She do! She do weigh three and a half pounds. That's pretty good for seven months because I was born five pounds."