University of Windsor women's basketball coach Chantal Vallee was one of the passengers aboard an Air Canada flight that was grounded over security concerns.

Vallee was on the flight from Toronto to  São Paulo, Brazil, that was forced to return to Pearson International Airport this morning amid security concerns.

"Flew away to São Paulo last night at 11:30 p.m to wake up this a.m ... back in Toronto airport surrounded by police," Vallee tweeted at 8 a.m. Thursday.

The flight departed the Toronto airport Wednesday night just before flights were grounded due to a security breach.

Pearson security

Chantal Vallee snapped this shot of police on her flight from Toronto to Brazil. (Courtesy Chantal Vallee)

A man slipped through security,  just before 11 p.m. ET, without being checked.

"We had been flying for about three hours when the plane turned around. We were told we were just passing over Florida," Vallee told Windsor Morning host Tony Doucette.

Vallee said the captain simply apologized before turning around and told the passengers he was just following orders.

"We didn’t even know there was a security breach. We were just told there was an issue with the Brazilian government," she said.

Vallee was recently named to the coaching staff of Brazil's Olympic women's basketball team.

She was off to join the team for the first time in São Paulo.

"Vans and cars of Police and border patrol [were] waiting for us in Toronto surrounding [the] airplane," Vallee wrote in an email to CBC News. "Then police officers in the plane came and arrested a man."

"We were told a security breach in Toronto forced us to return, but while in air, the captain had said it was Brazil demanding we couldn't land."

"When we landed, we heard a different story," Vallee later told Doucette.

Vallee said emptying the plane took more than an hour. She estimated that people disembarked in groups of five.

She was scheduled to fly out — again — at about 9:30 a.m. ET.