The Department of Veterans Affairs' internal watchdog has launched an investigation into a 10-day, taxpayer-funded trip taken by Secretary David Shulkin and his wife earlier this summer.

Shulkin came under fire last week for the July vacation to Denmark and the U.K., during which he and his wife attended a Wimbledon tennis match, and went shopping and sightseeing.

Though a conference on veterans policy and meetings with foreign officials were included in the trip, much of the secretary's time was spent touring castles in Copenhagen and enjoying a cruise with his wife.

Michael Nacincik, a spokesperson for the VA's Inspector General, told the Washington Examiner on Tuesday the internal watchdog is "gathering information and reviewing the secretary's recent trip." CBS News first reported the investigation.

Nacincik could not say how long the investigation is estimated to take or when it began.

"It really depends on what they find or what they don't find," he said.

Shulkin denied any wrongdoing in a statement last week, and announced that he would make the itinerary from his trip for the public.

"Veterans and taxpayers have a right to know about my official travel as secretary, and posting this information online for all to see will do just that," he said.

"The secretary welcomes the IG looking into his travel, and a good place to start would be VA's website where the VA posted his full foreign travel itineraries, along with any travel on a government or private aircraft," VA press secretary Curt Cashour later told CBS.

News of the IG investigation comes days after Health and Human Services Secretary Tom Price was fired for chartering several private flights on the taxpayer dime.

The Interior Department's internal watchdog also launched an investigation this week into Secretary Zinke's travel, bring the total number of Cabinet officials under investigation by their own agencies to four, including Treasury Secretary Steve Mnuchin and EPA administrator Scott Pruitt.